1. Field of the Invention
This invention relates to a method and an apparatus for combined-closed-cycle magnetohydrodynamic (MHD) generation which simultaneously uses an MHD generator and a gas turbine-generator unit, the heat source for the generation being fossil fuel such as coal and petroleum, nuclear energy such as energy released by fission or fusion, or solar energy. More particularly, the invention relates to durability improvement and size reduction of machinery for the combined-closed-cycle MHL generation, while retaining the high energy conversion efficiency of conventional combined-cycle MHD generation.
2. Related Art Statement
In conventional closed-cycle MHD generation, a suitable operative fluid, e.g., a rare gas, is heated to a high temperature by a high-temperature heat source, such as coal, petroleum, other suitable fossil fuel, nuclear fission energy, nuclear fusion energy, or solar energy. After added with a conductivity-improving seed agent is added to the rare gas, e.g., an alkali metal, the heated operative fluid is introduced into a magnetic field for conversion of the thermal energy thereof into electric energy through a magnetohydrodynamic process. The operative fluid is returned to the heat source after the conversion, so as to complete a closed-cycle of operative fluid.
The temperature of the operative fluid in closed-cycle MHD generation is much higher that the highest operating temperature of steam or gas in conventional thermal power plant machinery such as steam turbine-generator units or gas turbine-generator units. Hence, the closed-cycle MHD generation is suitable for use in combination with a high temperature heat source. Besides, the operative fluid outflowing from the MHD generator is still at a comparatively high temperature. Thus, it is generally preferred to connect a conventional generator unit downstream of the operative fluid from the MHD generator, which conventional generator unit operates at a lower temperature than the MHD generator. With the downstream generator unit, a closed-cycle of the operative fluid for combined generation is formed, and the energy of the high temperature heat source can be converted into electric energy at a high efficiency.
Two types of combined generation with the closed-cycle MHD generation have been proposed; namely, one type using a steam turbine-generator unit, and another type using a gas turbine-generator unit, the generator unit of either type being connected downstream of an MHD generator.
FIG. 2 shows an example of conventional combined generation using a steam turbine-generator unit connected to an MHD generator having a closed-cycle. In the example, a rare gas El heated to a high temperature at a heat source D is introduced to an MHD generator A1 for generating electric power. Post-operation rare gas E2 outflowing from the MHD generator A1 enters into a heat exchanger C1 and is cooled there. The cooled rare gas E3 enters into a compressor B and is compressed. Then, the compressed rare gas E4 returns to the heat source D, so that a closed-loop or closed-cycle of the rare gas E1 through E4 is completed.
On the other hand, the heat of the high-temperature rare gas E2 from the MHD generator A1 is transferred to water or vapor F at the heat exchanger C1, so as to produce heated vapor F1 which drives a steam turbine-generator unit A2 for generating electric power. The outflow vapor F2 from the steam turbine-generator unit A2 is condensed into water F3 by a condenser C2. The condensed water F3 is heated by the heat exchanger C1 as described above. Thus, a closed-loop or closed-cycle of water and vapor F1 through F3 is formed. The MHD generator A1 and the steam turbine-generator unit A2 are driven by the rare gas loop E1-E4 and the water and vapor loop F1-F3, respectively. The net electric output power is defined by the difference between the sum of outputs from the two generators Al and A2 and driving load power of the compressor B.
FIG. 3 shows an example of conventional combined generation using a gas turbine-generator unit connected to a closed-cycle MHD generator. In the example of FIG. 3, a rare gas E1 heated to a high temperature at a heat source D is introduced to an MHD generator A1 for producing electric power through the MHD process. Post-operation rare gas E2 outflowing from the MHD generator Al enters into a gas turbine-generator unit A3 for generating electric power. In this conventional arrangement, the gas turbine-generator unit A3 is disposed immediately downstream of the MHD generator A1. Exhaust rare gas E5 from the gas turbine-generator unit A3 enters into a heat exchanger C1 and is cooled there. The cooled rare gas E3 enters into a compressor B and is compressed. The compressed rare gas E4 is heated in the heat exchanger C1 by the above-mentioned exhaust rare gas E5 at a comparatively high temperature, and the heated rare gas E6 returns to the heat source D, so that a closed-loop or closed-cycle of the rare gas E1 through E6 is completed. Both of the MHD generator A1 and the gas turbine-generator unit A3 are driven by the rare gas loop E1-E6. The net electric output power is given by the difference between the sum of outputs from the two generators Al and A3 and driving load power of the compressor B.
As compared with the combined generation of FIG. 2 having heat losses at both cooling water lines for the compressor B and the condenser C2, the combined generation of FIG. 3 has a heat loss only at the cooling water line for the compressor B. Thus, the combined generation of FIG. 3 converts a larger portion of the heat energy input at the heat source D than that in the combined generation of FIG. 2, so that the energy conversion efficiency of combined generation of FIG. 3 is higher than that of FIG. 2.
Thus, with the combined generation of FIG. 2, the heat loss at the condenser C2 is added to the cooling water loss at the compressor B, and there is a limit in the ratio of output electric power to the input energy to the rare gas E from the heat source D. In short, the combined generation of FIG. 2 has a shortcoming in that the energy conversion efficiency of combined generation is comparatively low.
Despite that the energy conversion efficiency can be somewhat improved by the combined generation of FIG. 3 as pointed out above, the closed-loop generation of FIG. 3 has a shortcoming in that the compression ratio at the compressor B of FIG. 3 is required to be higher than that of FIG. 2. In particular, there is a certain preferred range of the pressure of the heated rare gas El to be introduced to the MHD generator Al depending on the intensity of the magnetic field thereat. On the other hand, the pressure of the cooled rare gas E3 entering the compressor B of FIG. 3 is lower than that in FIG. 2 because of the presence of the gas turbine-generator unit A3. Hence, to achieve the preferred range of the pressure, the compressor B of FIG. 3 must have a higher compression ratio than that of FIG. 2, and the compressor B of FIG. 3 becomes larger than that of FIG. 2.
Further, the post-operation rare gas E2 outflowing from the MHD generator Al contains alkali metal vapor as a seed agent, and such alkali metal vapor also enters into the gas turbine-generator unit A3 in FIG. 3. Thus, the closed-loop generation of FIG. 3 has another shortcoming in that the turbine blades of the gas turbine-generator unit A3 are susceptible to corrosion by the alkali metal vapor.